1. Technical Field
The present invention relates generally to multi-layer sliding bearings of the type having two or more metal layers bonded to a steel backing strip for use in journaling a shaft or the like.
2. Related Art
Sleeve or sliding bearings for use as main bearings or connecting bearings in internal combustion engines can be divided into two main categories. The categories: (1) bimetal bearings, which consist of a steel backing and a lining alloy on the inside diameter; (2) trimetal bearings, which include a third layer which is typically electro deposited over the lining alloy.
Bimetal bearings typically include an aluminum based lining material placed on the inside diameter of a bearing. This type of bearing offers advantages over trimetal bearings including low cost, good wear resistance, and excellent corrosion resistance. However, for more severe applications, such as in today""s higher output engines, there is a need for a bearing with a high fatigue strength and excellent sliding properties which cannot be achieved utilizing bimetal bearings having an aluminum based lining. Typically, trimetal bearings which exhibit a higher fatigue strength than most bimetal bearings must be utilized in the more severe applications.
Several factors known in the art for improving the fatigue strength and performance of bearings include: (a) inclusion of a soft phase, such as tin or lead within the alloy layer to impart seizure resistance to the lining alloy; (b) inclusion of hard particles within the aluminum alloy such as silicon to increase the wear and seizure resistance of the alloy; (c) inclusion of an interlayer between the aluminum bearing alloy and the steel backing to achieve bonding between the lining and the steel when the amount of the soft phase exceeds about 10% by weight.
For example, U.S. Pat. No. 5,112,416 discloses an aluminum-based alloy bearing having an intermediate bonding layer where the hardness is lower than 40% of the aluminum-based bearing alloy in terms of Vickers hardness. While the U.S. Pat. No. 5,112,416 demonstrates a bimetal aluminum bearing, there is no disclosure that such could operate under high load, high fatigue conditions. The highest known fatigue strength shown by any prior bi-metal aluminum bearings is less than 90 mega pascals.
A sliding bearing constructed according to the invention has a steel backing on which a bi-metal lining is bonded. The lining includes an aluminum-based bearing layer and an intermediate layer of aluminum-based metal disposed between the bearing layer and the steel backing. The composite bearing material exhibits a fatigue strength of at least 90 MPa.
The invention has the advantage of providing a bi-metal aluminum bearing with a fatigue strength at a level normally associated with traditional tri-metal bearings.
The bearing material has the further advantage of providing an aluminum-based bearing layer that has a fine microstructure; thereby improving the fatigue strength of a bearing produced from the composite bearing material.
There is also disclosed a method of manufacturing a composite bearing including the steps of: a) casting an aluminum alloy to produce an aluminum-based bearing layer having silicon particles of less than 4 microns in average diameter dispersed uniformly therein, and a soft phase having a maximum length of 250 microns; b) cladding an aluminum-based intermediate layer material to said aluminum-based bearing layer to produce a bi-metal lining; and c) hot bonding a steel backing layer to said bi-metal lining.